Also, according to Brown and Roberts in "Every Insult and Indignity" their guns shoot about 4" low at 200 yards. Period sources indicate that British guns of the period were sighted to zero at 200 yards. A slightly larger ball *might* reduce the drop over that distance.
Steve
That is a possibility, but I think other factors are more important. The quality of the powder is the most important in my opinion. British rifle companies were issued "superfine, double strength, powder", which was most probably "hotter" than what we have commonly available to us today. This would explain the vast improvement I have found with the rifle with the use of the Swiss powder over the weaker Goex powder. Some even have theorized that the British rifle powder could be more closely replicated by mixing 4F and 3F together (read Bailey's military flintlock rifles book). Although I don't recommend someone doing that, it does indicate a need for a hotter powder to get these rifles to perform correctly.
I first came across the powder issue when trying to get original breech loading British double rifles and shotguns to perform up to acceptable levels. I have found that using the more powerful, fast burning, Swiss 3F powder is crucial in getting these old guns to regulate properly. Most of the powders we have available to us today are not even close to the old sporting powders of centuries past.
The other reason I don’t believe a larger ball was used, was simply due to the very conservative nature of the British military in general. If there was new rifle being made, whether it’s a Ferguson or any other one, it must be made to pattern dictated by the Crown. In that era, a rifle must be made to shoot a carbine ball (.615). I can’t imagine the Crown allowing a new rifle (that they didn’t really want in the first place) to use an unique size of ammunition.
Now if historic accuracy is not a concern, by all means experiment with different sized balls. If finding the absolute best load combination is of utmost importance, playing around with loads is half the fun. In my specific gun I cannot improve upon the results of using the .615 ball, but like all guns, each one can be different.